The objective of this project is the study of basic biophysical processes which affect the electrical activity of the heart, and determine its reflection in epicardial and body surface potentials. This will be achieved through the development of theoretical (computer) model simulation. Specific aims are: (1) The reconstruction of epicardial potentials from body surface potential distributions. This will permit a non-invasive, detailed examination of regional electrical events within the heart (site of origin of arrhythmids, location of pre-excitation in WPW syndrome, location and size of ischemic and infarcted regions, nature of conduction abnormalities). (2) The generation of activation isochrones, and the computation of epicardial potentials for a variety of (normal and abnormal) potentials. This will permit the study of volume conductor effects, and will enhance our understanding of the relationships between surface potentials, epicardial potentials, and cardiac events. The simulation studies will enhance the research and diagnostic capacity of both body surface and epicardial potentials. The models will be utilized in the interpretation of clinical body surface potential maps, obtained with a simultaneous 180 electrode mapping system.